Northern peatlands contain a large terrestrial carbonpool that plays an important role in the Earth’s carbon cycle.A considerable fraction of this carbon pool is currentlyin permafrost and is biogeochemically relatively inert; thiswill change with increasing soil temperatures as a result ofclimate warming in the 21st century. We use a geospatiallyexplicit representation of peat areas and peat depth from arecently-compiled database and a geothermal model to estimatenorthern North America soil temperature responses topredicted changes in air temperature. We find that, despite awidespread decline in the areas classified as permafrost, soiltemperatures in peatlands respond more slowly to increasesin air temperature owing to the insulating properties of peat.We estimate that an additional 670 km3 of peat soils in NorthAmerica, containing 33 Pg C, could be seasonally thawedby the end of the century, representing 20% of the totalpeat volume in Alaska and Canada. Warming conditions resultin a lengthening of the soil thaw period by 40 days,averaged over the model domain. These changes have potentiallyimportant implications for the carbon balance of peatsoils.